Known technologies in this field are described, for example, in JP-A-2002-162348, and Hideo Nakae and two others, Reza Henikei o Mochiita Henjo Kokuen Chutetsu no Hamen Kaiseki ni yoru Kokuen Keitai no Hantei (Evaluation of graphite shape by fracture surface analysis of graphite cast iron using laser displacement meter), Chuzo Kogaku, Japan Foundry Engineering Society, Vol. 74, 2002, No. 10, Pages 644-649. The conventional technologies comprise basic steps of irradiating a fracture surface of a cast iron with a laser light, measuring the surface roughness of the fracture surface, and evaluating shape, distribution, etc. of graphite pieces contained in the structure based on the surface roughness.
The above conventional technologies are the most promising methods in practical use among the known graphite structure evaluation methods. However, in the technologies, a resultant graph must be directly read to obtain final evaluation results, whereby the technologies are disadvantageous in that there are often differences between individuals in the results and that it is difficult to imagine the graphite structure by the results, thus there being still room for improvement.